Process and apparatus for separation and purification of conjugated diene

ABSTRACT

A method of separating and purifying conjugated diene, including the steps of: obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in a lower boiling distillation column  14 ; obtaining a second bottom product and distillation portion by distilling said first bottom product under an environment in the presence of a polymerization inhibitor in a higher boiling distillation column  16 ; measuring concentration of a polymerization inhibitor included in said first bottom product and second bottom product respectively; controlling the concentration of the polymerization inhibitor included in said first bottom product and/or second bottom product by changing a supply amount of the polymerization inhibitor to said lower boiling distillation column  14  and/or higher boiling distillation column  16  in accordance with said measured concentration of the polymerization inhibitor included in said first bottom product and second bottom product respectively; measuring concentration of a polymerization inhibitor included in said distillation portion; and controlling the concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said higher boiling distillation column  16  in accordance with said measured concentration of the polymerization inhibitor included in distillation portion. The method allows the suppression of generation of a popcorn polymer in the apparatus with good efficiency and stability.

TECHNICAL FIELD

The present invention relates to a method and apparatus for separating and purifying conjugated diene capable of efficiently suppressing generation of popcorn polymer inside a purification apparatus when separating and purifying high purity isoprene, butadiene and other conjugated diene from petroleum distillates.

BACKGROUND ART

Conjugated diene, such as 1,3-butadiene, isoprene and chloroprene as unsaturated hydrocarbons, are liable to accidentally generate porous insoluble polymer, known as popcorn polymer, both in liquid and gas phases. Particularly, industrial distillation satisfies various conditions liable to generate the popcorn polymer, such as suitable temperature at operation, high purity monomer, coexistence of gas and liquid phases, moisture ingredient, and existence of iron rust. Once this popcorn polymer generates, it is made to a core and the popcorn polymer exponentially increases around the core leading rapid blockage in an apparatus. Also, this polymer is strong that it is insoluble in all known solvent and do not melt even heated. In order to remove this polymer, there is no other suitable process but cleaning by mechanical means. This cleaning requires to suspend the apparatus for a time and unable to avoid the economical disadvantage.

Moreover, the mechanical cleaning cannot completely remove the polymer that when the operation begins, a small amount of polymer that was left behind is made to the core and the polymer increases again. As a method of preventing polymerization of conjugated diene inside a separation and purification apparatus, a variety of proposals have been made. For example, the Japanese Unexamined Patent Publication No. 50-112304 discloses a method of distilling C5 hydrocarbon in the presence of a di-lower alkylhydroxylamine and it describes the method allows the suppression of generation of a popcorn polymer at distillation of isoprene.

Also, the Japanese Unexamined Patent Publication No. 56-81526 discloses a method of extractive distillation in the presence of furfural and a furfural condensation product in an extracting solvent. Furthermore, the Japanese Examined Patent Publication No. 45-19682 discloses a method of extractive distillation for conjugated diene hydrocarbon by adding a polymerization inhibitor or a polymerization chain transfer agent in an extracting solvent. In here, it discloses that adding a polymerization inhibitor or a polymerization chain transfer agent in an extracting solvent is also possible.

However, according to the method described in these publications, a more than necessary amount of a polymerization inhibitor was added to suppress generation of popcorn polymer inside the apparatus in some cases, consequently, costs of separation and purification was tend to rise.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method and apparatus for separating and purifying conjugated diene, capable of efficiently and stably suppressing generation of popcorn polymer in the apparatus.

(1) To attain the above object, according to a first aspect, a method of separating and purifying conjugated diene, comprises the steps of

obtaining a bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in a distillation column;

measuring concentration of a polymerization inhibitor included in said bottom product; and

controlling the concentration of the polymerization inhibitor included in said bottom product by changing a supply amount of the polymerization inhibitor to said distillation column in accordance with the measured concentration of the polymerization inhibitor.

In a method of separating and purifying according to the first aspect, a method of separating and purifying according to a second aspect described below is preferable.

According to the second aspect, a method of separating and purifying conjugated diene comprises the steps of

obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in a lower boiling distillation column;

obtaining a second bottom product by distilling said first bottom product under an environment in the presence of the polymerization inhibitor in a higher boiling distillation column;

measuring each of concentrations of the polymerization inhibitors included in said first bottom product and second bottom product; and

controlling the concentration of the polymerization inhibitor included in said first bottom product and/or second bottom product by changing a supply amount of the polymerization inhibitor to said lower boiling distillation column and/or higher boiling distillation column in accordance with the measured concentration of the polymerization inhibitor.

(2) To attain the above object, according to a third aspect, a method of separating and purifying conjugated diene, comprises the steps of

obtaining a distillation portion by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in a distillation column;

measuring concentration of a polymerization inhibitor included in said distillation portion; and

controlling the concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said distillation column in accordance with the measured concentration of the polymerization inhibitor.

In a method of separating and purifying according to the third aspect, a method of separating and purifying according to a forth aspect described below is preferable.

According to the forth aspect, a method of separating and purifying conjugated diene comprises the steps of

obtaining a bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene in a lower boiling distillation column;

obtaining a distillation portion by distilling said bottom product under an environment in the presence of the polymerization inhibitor in a higher boiling distillation column;

measuring concentration of a polymerization inhibitor included in said distillation portion; and

controlling the concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said higher boiling distillation column in accordance with the measured concentration of the polymerization inhibitor.

(3) In a method of separating and purifying according to the first to forth aspect, an invention according to a fifth aspect described below is preferable.

According to the fifth aspect, a method of separating and purifying conjugated diene comprises the steps of

obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in a lower boiling distillation column;

obtaining a second bottom product and a distillation portion by distilling the first bottom product under an environment in the presence of a polymerization inhibitor in a higher boiling distillation column;

measuring each of concentrations of the polymerization inhibitors included in the first bottom product and second bottom product;

controlling the concentration of the polymerization inhibitor included in the first bottom product and/or second bottom product by changing a supplying amount of the polymerization inhibitor to said lower boiling distillation column and/or higher boiling distillation column in accordance with the measured concentration of the polymerization inhibitor included in the first bottom product and second bottom product;

measuring concentration of a polymerization inhibitor included in said distillation portion; and

controlling the concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said higher boiling distillation column in accordance with the measured concentration of the polymerization inhibitor included in the distillation portion.

(4) To attain the above object, an apparatus for separating and purifying conjugated diene according to the first aspect comprises

a distillation column for obtaining a bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor;

a measurement means for measuring concentration of a polymerization inhibitor included in the bottom product;

a supply system for supplying a polymerization inhibitor newly to the distillation column; and

a control means for controlling the concentration of the polymerization inhibitor included in the bottom product by changing a supply amount of the polymerization inhibitor to the distillation column in accordance with the measured concentration of the polymerization inhibitor.

In an apparatus for separating and purifying according to the first aspect, an apparatus for separating and purifying according to a second aspect described below is preferable.

An apparatus for separating and purifying conjugated diene according to the second aspect comprises

a lower boiling distillation column for obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor;

a higher boiling distillation column for obtaining a second bottom product by distilling the first bottom product under an environment in the presence of a polymerization inhibitor;

a measurement means for measuring each of concentrations of the polymerization inhibitors included in the first bottom product and second bottom product respectively;

a supply system for supplying a polymerization inhibitor newly to the lower boiling distillation column and/or higher boiling distillation column; and

a control means for controlling the concentration of the polymerization inhibitor included in the first bottom product and/or second bottom product by changing the supply amount of the polymerization inhibitor to the lower boiling distillation column and/or higher boiling distillation column in accordance with the measured concentration of the polymerization inhibitor.

(5) To attain the above object, an apparatus for separating and purifying conjugated diene according to the third aspect comprises

a distillation column for obtaining a distillation portion by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor;

a measurement means for measuring concentration of a polymerization inhibitor included in the distillation portion;

a supply system movable in an up-and-down motion for supplying a polymerization inhibitor to the distillation column; and

a control means for controlling the concentration of the polymerization inhibitor included in the distillation portion by changing a supplying stage of the polymerization inhibitor to the distillation column in accordance with the measured concentration of the polymerization inhibitor.

In an apparatus for separating and purifying according to the third aspect, an apparatus for separating and purifying according to a forth aspect described below is preferable.

An apparatus for separating and purifying conjugated diene according to the forth aspect comprises

a lower boiling distillation column for obtaining a bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene;

a higher boiling distillation column for obtaining a distillation portion by distilling the bottom product under an environment in the presence of a polymerization inhibitor;

a measurement means for measuring concentration of a polymerization inhibitor included in the distillation portion;

a supply system movable in an up-and-down motion for supplying a polymerization inhibitor to the higher boiling distillation column; and

a control means for controlling the concentration of the polymerization inhibitor included in the distillation portion by changing a supplying stage of the polymerization inhibitor to the higher boiling distillation column in accordance with the measured concentration of the polymerization inhibitor.

(6) In an apparatus for separating and purifying according to the first to forth aspects, an apparatus for separating and purifying according to a fifth aspect described below is preferable.

An apparatus for separating and purifying conjugated diene according to the fifth aspect comprises

a lower boiling distillation column for obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor;

a higher boiling distillation column for obtaining a second bottom product and a distillation portion by distilling the first bottom product under an environment in the presence of a polymerization inhibitor;

a measurement means for measuring each of concentrations of the polymerization inhibitors included in the first bottom product and the second bottom product respectively;

a first supply system for supplying a polymerization inhibitor newly to the lower boiling distillation column and/or higher boiling distillation column;

a control means for controlling the concentration of the polymerization inhibitor included in the first bottom product and/or second bottom product by changing a supplying amount of the polymerization inhibitor to the lower boiling distillation column and/or higher boiling distillation column in accordance with the measured concentration of the polymerization inhibitor included in the first bottom product and second bottom product respectively;

a measurement means for measuring concentration of a polymerization inhibitor included in the distillation portion;

a second supply system movable in an up-and-down motion for supplying a polymerization inhibitor to the higher boiling distillation column; and

a control means for controlling the concentration of the polymerization inhibitor included in the distillation portion by changing a supplying stage of the polymerization inhibitor to the higher boiling distillation column in accordance with the measured concentration of the polymerization inhibitor included in the distillation portion.

(7) In the present invention, it is preferable to use an analyzing apparatus, such as an ion chromatograph, a liquid chromatograph and a gas chromatograph, for measuring concentration of the polymerization inhibitor.

In the present invention, as a method of changing a supply amount of a polymerization inhibitor to a distillation column, for example, when the measured concentration of the polymerization inhibitor exceeds the upper limit value of a reference range, the supply amount of the polymerization inhibitor to the distillation column may be decreased, while when the measured concentration of the polymerization inhibitor is below the lower limit value of the reference range, the supply amount of the polymerization inhibitor to the distillation column may be increased. In the present invention, a means to change the supply amount of the polymerization inhibitor to the distillation column may be manually controlled or automatically controlled.

In the present invention, as a method of changing a supplying stage of a polymerization inhibitor to a distillation column, for example, when the measured concentration of the polymerization inhibitor exceeds the upper limit value of a reference range, the supplying stage of the polymerization inhibitor to the distillation column may be lowered, while when the measured concentration of the polymerization inhibitor is below the lower limit value of the reference range, the supplying stage of the polymerization inhibitor to the distillation column may be raised. In the present invention, a means to change the supplying stage of the polymerization inhibitor to the distillation column may be manually controlled or automatically controlled.

(8) A hydrocarbon mixture including conjugated diene, which can be applied to the present invention is normally a hydrocarbon mixture including conjugated diene of C4 or more obtained by cracking naphtha and separating ethylene, propylene and other C2 and C3 hydrocarbons, preferably a C4 hydrocarbon fraction or C5 hydrocarbon fraction, more preferably a C4 hydrocarbon fraction including butadiene or a C5 hydrocarbon fraction including isoprene.

In a hydrocarbon mixture including conjugated diene, which can be applied to the present invention, the content(concentration) of conjugated diene is previously heightened by extractive distillation or so. In this case, conjugated diene included in the hydrocarbon mixture is normally, 80% or more, preferably, 90% or more, and more preferably, 95% or more.

(9) A polymerization inhibitor, which can be used in the present invention, is used for suppressing generation of popcorn polymer inside the apparatus and not particularly limited.

Concretely, as to inhibit and suppress polymerization by scavenging radicals with stable radicals, 1,1-diphenyl-2-picrylhydrazyl, 1,3,5-triphenyl ferudazyl, 2,6-di-t-butyl-α-(3,5-di-t-butyl-4-oxo-2,5-cyclohexanediene-1-indene)-p-tolyloxy, 2,2,6,6-tetramethyl-4-piperidone-1-oxyl, N-(3-N-oxyanilino-1,3-dimethylbutylidene)-aniline oxide, 2-(2-cyanopropyl)-ferudazyl; as to inhibit and suppress polymerization by chain transfer reaction, ones having activated NH-bond such as diphenylpicrylhydrazine, diphenylamine, diethylhydroxylamine, dimethylhydroxylamine, methylethylhydroxylamine, dipropylhydroxylamine, dibutyhydroxylamine, dipentylhydroxylamine; ones having OH-bond of phenol such as hydroquinone and t-butylcatechol; ditiobenzoyldisulfide, p,p′-ditolyl trisulfide, p,p′-ditolyl tetrasulfide, dibenzyl tetrasulfide, tetraethylthiuram disulfide; as to inhibit and suppress polymerization by addition reaction, oxygen, sulfur, anthracene, 1,2-benzanthracene, tetracene; benzoquinone derivatives such as chloranil, p-benzoquinone, 2,6-dichlorbenzoquinone, 2,5-dichlor benzoquinone, nitro compounds such as furfurylidene-malononitrile and m-dinitrobenzene, nitroso compounds such as nitrosobenzene, 2-methyl-2-nitrosopropane; further, metal salts such as ferric chloride and ferric bromide are exemplified.

Out of the above polymerization inhibitors, ones that inhibit and suppress the polymerization by chain transfer reaction, particularly di-lower aklylhydroxylamine is preferable. Concretely, diethylhydroxylamine is preferable.

Further, these polymerization inhibitors may be used alone or in combination of two or more. An amount of the polymerization inhibitors is normally 0.1 to 200 ppm based on weight of a hydrocarbon mixture including conjugated diene. A method of using a polymerization inhibitor is not particularly limited and may be attained by simply bringing conjugated diene or a hydrocarbon mixture including conjugated diene contact the polymerization inhibitor.

Operation and Effect of the Invention

In a method of separating and purifying conjugated diene by using separating and purifying apparatus according to the first and second aspects, concentration of a polymerization inhibitor included in a bottom product taken out after a distillation is measured, and an supplying amount of the polymerization inhibitor to a distillation column is changed based thereon. Therefore, it is possible to supply a polymerization inhibitor in just proportion required for suppressing generation of popcorn polymer inside the apparatus, and generation of popcorn polymer can be efficiently and stably suppressed. As a result, costs of separating and purifying conjugated diene can be reduced comparing with that in the conventional techniques.

In a method of separating and purifying conjugated diene by using separating and purifying apparatus according to the third and forth aspects, concentration of a polymerization inhibitor included in a distillation portion taken out after a distillation is measured, and the polymerization inhibitor supplying stage to a distillation column is changed based thereon. Therefore, it is possible to supply a polymerization inhibitor in the most suitable position required for suppressing generation of popcorn polymer inside the apparatus, and generation of popcorn polymer can be efficiently and stably suppressed. As a result, costs of separating and purifying conjugated diene can be reduced comparing with that in the conventional techniques, moreover, concentration of the polymerization inhibitor in purified conjugated diene can be suppressed low.

In a method of separating and purifying conjugated diene by using separating and purifying apparatus according to the fifth aspects, generation of popcorn polymer can be more efficiently and more stably suppressed. As a result, costs of separating and purifying conjugated diene can be much reduced comparing with that in the conventional techniques.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 is a block diagram showing an example of a separation and purification system using a separation and purification apparatus according to the present invention. 2 a separation and purification system 8 an extractive distillation column 8d to 8e, 8h a line 82a a reflux line 8i a supply amount adjustment valve 14 a lower boiling distillation column 16 a higher boiling distillation column 16a to 16d, 16f a line 162a a reflux line 163a a condenser 16e a supply amount adjustment valve 22a, 22b a control device (control means) 18a to 18c a liquid chromatograph or gas chromatograph analyzing device (measurement device)

BEST MODE FOR CARRYING OUT THE INVENTION

Below, an apparatus for separating and purifying conjugated diene and a method of separating and purifying conjugated diene according to the present invention will be explained in detail based on embodiments shown by the drawings. In the present embodiment, as an example of an apparatus for separating and purifying conjugated diene, an explanation will be made by taking an example of a separation and purification apparatus used for purifying a highly concentrated butadiene from C4 hydrocarbon fraction in which the concentration of butadiene is previously heightened by extractive distillation or so.

Separation and Purification System 2

As shown in FIG. 1, a separation and purification system 2 according to the present embodiment comprises a lower boiling distillation column 14 and a higher boiling distillation column 16. The lower boiling distillation column 14 is a column for performing distillation of a C4 hydrocarbon fraction in which the concentration of butadiene is heightened and taking out a first distillation portion and a first bottom product, which is connected to the later explained higher boiling distillation column 16 by a line 16 a. The line 16 a is provided with a liquid chromatograph or gas chromatograph analyzing device (measurement device) 18 a for measuring concentration of a polymerization inhibitor included in the first bottom product flowing there, and the measured concentration of the polymerization inhibitor is sent as a predetermined output signal to the control device (control means) 22 a. According to the present embodiment, in a reflux line 82 a provided near the top of the column body of extractive distillation column 8, a line 8 h for supplying a polymerization inhibitor is connected.

On the line 8 h, a supply amount adjustment valve 8 i for adjusting a supply amount of the polymerization inhibitor is provided, and a supply amount of the polymerization inhibitor can be adjusted based on an output signal sent from a control device 22 a.

The lower boiling distillation column 14 generally comprises a column body, a condenser for cooling vapor exhausted from top of the column body and condensing to a liquid, a reflux drum for storing the distillation portion condensed to a liquid by the condenser, a reflux line for re-supply a part of the distillation portion stored in the reflux drum to near the top of the column body, and a re-boiler arranged at the bottom of the column body, but they are omitted in the drawing in the present embodiment. A form of the distillation column may be, for example, any of a plate column wherein inside the column body is divided by horizontal stage trays, so that contact of the liquid and vapor is made gradually, or a packed column filled with filler for efficient material movement between different phases, etc. Accuracy of distillation (ability of separating those having close boiling points) becomes higher as the number of stage trays becomes larger; however, when the number is too large, the cost is increased, so that it is selected in consideration of balance of the ability and the cost.

Note that the reference number “8 d” in FIG. 1 is a line of taking out the extractive solvent from an extractive distillation column 8 at the bottom of the column body and the reference number “16 f” is a line of taking out the first distillation portion from the reflux drum (not shown).

The higher boiling distillation column 16 is a column for distilling a first bottom product supplied through the line 16 a and taking out a second distillation portion and a second bottom product. Near the upper stage of the higher boiling distillation column 16, a line 16 d for supplying polymerization inhibitor is connected. Namely, according to the present embodiment, line 16 d is not connected to reflux line 162 a wherein the second distillation portion is taken out from the top of the column body of higher boiling distillation portion 16. Moreover, according to the present embodiment, connecting position of line 16 d to the higher boiling distillation column 16, namely, supplying position of the polymerization inhibitor to the higher boiling distillation column 16 is movable in up-and-down motion in response to an output signal from the control device 22 b. The line 16 d is provided with a supply amount adjustment valve 16 e for adjusting a supply amount of the polymerization inhibitor, and the supply amount of the polymerization inhibitor can be adjusted based on an output signal sent from the control device 22 a.

Near the upper stage of the higher boiling distillation column 16, a line 16 c for taking out the second distillation portion is connected. The line 16 c is provided with a liquid chromatograph or a gas chromatograph analyzing device (measurement device) 18 c for measuring concentration of a polymerization inhibitor included in the second distillation portion flowing there, and the measured concentration of the polymerization inhibitor is sent as a predetermined output signal to the control device (control means) 22 b. Near the bottom stage of the higher boiling distillation column 16, a line 16 b for taking out the second bottom product is connected. The line 16 b is provided with a liquid chromatograph or a gas chromatograph analyzing device (measurement device) 18 b for measuring concentration of a polymerization inhibitor included in the second bottom product flowing there, and the measured concentration of the polymerization inhibitor is sent as a predetermined output signal to the control device (control means) 22 a. A form of the higher boiling distillation column 16, as mentioned above, may be a plate column or a packed column. When using a plate column, the number of stage trays is selected in consideration of balance of the ability and the cost as in the same way with the lower boiling distillation column 14 mentioned above.

Effects

A separation and purification system 2 according to the present embodiment exhibits effects below.

The lower boiling distillation column 14 is supplied with a C4 hydrocarbon fraction in which the concentration of butadiene is heightened through a line 8 e and a reflux line 82 a arranged at near the top of the extractive distillation column 8. Moreover, the lower boiling distillation column 14 is supplied with the polymerization inhibitor through line 8 e, which is from line 8 h and mixed with the C4 hydrocarbon fraction in reflux line 82 a. A position of supplying the C4 hydrocarbon fraction and the polymerization inhibitor to the lower boiling distillation column 14 is not particularly limited, but normally at an approximate middle stage. Further, the polymerization inhibitor is preferably supplied before a condenser in the reflux line 82 a and mixed with the C4 hydrocarbon fraction. However, the polymerization inhibitor may be supplied from the other position, such as line 8 e. Also, the line 8 h may be directly connected to the lower boiling distillation column 14 and the polymerization inhibitor and C4 hydrocarbon fraction may be supplied separately. Along with the supply of the C4 hydrocarbon fraction and the polymerization inhibitor, distillation is performed by heating by the re-boiler (not shown) arranged at the bottom of the lower boiling distillation column 14. A pressure inside the lower boiling distillation column 14 is not particularly limited and is normally 4 to 6 atms, and a temperature at the bottom is a boiling point under the pressure. From the top of the lower boiling distillation column 14, a distillation portion including much methyl acetylene is taken out, the distillation portion is condensed in the condenser (not shown), a part thereof is refluxed to be return to the top of the lower boiling distillation column 14, and the remaining portion is taken out as a first distillation portion through line 16 f. On the other hand, from the bottom of the lower boiling distillation column 14, fraction including much high butadiene, cis-2-butene and pentene taken out as the first bottom product and supplied to the higher boiling distillation column 16 through the line 16 a. And the higher boiling distillation column 16 is supplied with the polymerization inhibitor through line 16 d.

A position of supplying the first bottom product to the higher boiling distillation column 16 is not particularly limited, but normally at an approximate middle stage and a position of supplying the polymerization inhibitor to the higher boiling distillation column 16 is preferably at an upper stage.

The polymerization inhibitor used in here is not preferable to mix with a high purity butadiene, which may be a material of polybutadiene. When the supplying position of the polymerization inhibitor became higher, the effect of the polymerization inhibitor on the popcorn polymer also became high, however, the polymerization inhibitor was liable to mix with a high purity butadiene. When the supplying position of the polymerization inhibitor became lower, the polymerization inhibitor was difficult to mix with a high purity butadiene, however, the effect of the polymerization inhibitor on the popcorn polymer also became low.

Concretely, for instance, when the high boiling distillation column 16 is used as a plate column, the supplying position is preferably the first stage from the top. Along with the supply of the first bottom product and the polymerization inhibitor, distillation is performed by heating with the re-boiler (not shown) arranged at the bottom of the higher boiling distillation column 16. A pressure in the higher boiling distillation column 16 is not particularly limited, but normally is 4 to 6 atms, and a temperature at the bottom is a boiling point under the pressure. From the bottom of the higher boiling distillation column 16, fraction including much high cis-2-butene and pentene are taken out as the second bottom product and recovered through line 16 b.

On the other hand, a fraction including much highly concentrated butadiene is taken out from the top of the higher boiling distillation column 16, and the fraction is condensed in the condenser 163 a. A part thereof is returned to the top of the higher boiling distillation column 16 through the reflux line 162 a, and the remaining portion is taken out as a distillation portion through line 16 c. Finally, the second distillation portion taken out from the line 16 c is supplied as high purity butadiene to a material of polybutadiene, etc.

In the present embodiment, the line 16 a is provided with a liquid chromatograph or a gas chromatograph analyzing device (measurement device) 18 a for measuring concentration of a polymerization inhibitor included in the first bottom product. The measured concentration of the polymerization inhibitor is sent as an output signal (a concentration value) to the control device 22 a, where the concentration value is compared with a reference range (concentration in a predetermined range). The concentration of the reference range depends on the kind of the polymerization inhibitor, however, with diethylhydroxylamine, preferably 1 to 20 ppm, more preferably 5 to 10 ppm. As a result, when the actually measured concentration value is judged to be over the upper limit value, the control device 22 a sends to the valves 8 i a signal to decrease a supply amount of the polymerization inhibitor to the lower boiling distillation column 14. Inversely, when the concentration of the polymerization inhibitor included in the first bottom product flowing in the line 16 a is judged to be under the lower limit, the control device 22 a sends to the valves 8 i a signal to increase the supply amount of the polymerization inhibitor to the lower boiling distillation column 14. In the present embodiment, as explained above, on-off control is made to adjust the concentration of the polymerization inhibitor included in the first bottom product flowing in the line 16 a to be in a reference range, but it may be controlled by other control algorithm, for example, proportional control, proportional integral control, proportional integral differentiation control, fuzzy control and adaptive control, etc.

In the present embodiment, the line 16 b is provided with a liquid chromatograph or a gas chromatograph analyzing device (measurement device) 18 b for measuring concentration of a polymerization inhibitor included in the second bottom product. The measured concentration of the polymerization inhibitor is sent as an output signal (a concentration value) to the control device 22 a, where the concentration value is compared with a reference range (concentration in a predetermined range). The concentration of the reference range depends on the kind of the polymerization inhibitor, however, with diethylhydroxylamine, preferably 500 to 10000 ppm, more preferably 1500 to 8000 ppm. As a result, when the actually measured concentration value is judged to be over the upper limit value, the control device 22 a sends to the valves 16 e a signal to decrease a supply amount of the polymerization inhibitor to the higher boiling distillation column 16. After a predetermined time under these conditions, when the concentration of the polymerization inhibitor included in the second bottom product flowing in the line 16 b is judged to be under the lower limit, the control device 22 a sends to the valves 16 e a signal to increase the supply amount of the polymerization inhibitor to the higher boiling distillation column 16.

In the present embodiment, as explained above, on-off control is made to adjust the concentration of the polymerization inhibitor included in the second bottom product flowing in the line 16 b to be in a reference range, but it may be controlled by other abovementioned control algorithm. Further, in the present embodiment, the line 16 c is provided with a liquid chromatograph or a gas chromatograph analyzing device (measurement device) 18 c for measuring concentration of a polymerization inhibitor included in the second distillation portion. The measured concentration of the polymerization inhibitor is sent as an output signal (a concentration value) to the control device 22 b, where the concentration value is compared with a reference value. The reference value is preferably 2 ppm or less, more preferably 1 ppm or less. As a result, when the actually measured concentration value is judged to be over the reference value, the control device 22 b sends to the line 16 d a signal to lower a supplying stage of the polymerization inhibitor to the higher boiling distillation column 16.

In the present embodiment, as explained above, on-off control is made to adjust the concentration of the polymerization inhibitor included in the second distillation portion flowing in the line 16 c to be in a reference value, but it may be controlled by other abovementioned control algorithm.

Note that the measuring concentration of the polymerization inhibitor, as mentioned above, is not necessarily done on an on-line. The measuring may be performed on an off-line, namely, taking out a small amount of the distillation portion from each line, measuring concentration of the distillation portion at different place, and inputting the measurement result to the control devices 22 a and 22 b.

According to the separation and purification system 2 according to the present embodiment exhibits effects above, it is possible to supply a polymerization inhibitor in just proportion required for suppressing generation of popcorn polymer, and generation of popcorn polymer can be efficiently and stably suppressed. As a result, high purity butadiene can be separated and purified at a lower cost comparing with the conventional cases.

Also, in the present embodiment, by measuring concentration of the polymerization inhibitor included in the first and the second bottom products flowing in line 16 a and line 16 b and the second distillation portion taken out from line 16 c using a liquid chromatograph and a gas chromatograph analyzing devices 18 a to 18 c, measurement of the concentration of the polymerization inhibitor can be made easily and efficiently. Note that in the present embodiment, since an output signals are continuously sent from the analyzing devices 18 a and 18 b to the control device 22 a and from the analyzing device 18 c to the control device 22 b respectively, the above operations are also continuously performed in the control devices 22 a and 22 b. However, a method in which the measurement interval is set to several hours to several days to send the signals to the control devices 22 a and 22 b (digital controlling) is more economical.

Embodiments of the present invention were explained above, but the present invention is not limited to the embodiments at all and may be naturally carried out in various embodiments within the scope of the present invention. For example, in the above embodiment, butadiene is separated and purified from C4 hydrocarbon fraction, but isoprene may also be separated and purified from C5 hydrocarbon fraction. 

1. A method of separating and purifying conjugated diene, comprising the steps of: obtaining a bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in an distillation column; measuring concentration of a polymerization inhibitor included in said bottom product; and controlling the concentration of the polymerization inhibitor included in said bottom product by changing a supply amount of the polymerization inhibitor to said distillation column in accordance with said measured concentration of the polymerization inhibitor.
 2. A method of separating and purifying conjugated diene, comprising the steps of: obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in a lower boiling distillation column; obtaining a second bottom product by distilling said first bottom product under an environment in the presence of a polymerization inhibitor in a higher boiling distillation column; measuring each of concentrations of the polymerization inhibitors included in said first bottom product and second bottom product respectively; and controlling the concentration of the polymerization inhibitor included in said first bottom product and/or second bottom product by changing a supply amount of the polymerization inhibitor to said lower boiling distillation column and/or higher boiling distillation column in accordance with said measured concentration of the polymerization inhibitor.
 3. A method of separating and purifying conjugated diene, comprising the steps of: obtaining a distillation portion by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in an distillation column; measuring concentration of a polymerization inhibitor included in said distillation portion; and controlling the concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said distillation column in accordance with said measured concentration of the polymerization inhibitor.
 4. A method of separating and purifying conjugated diene, comprising the steps of: obtaining a bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene in a lower boiling distillation column; obtaining a distillation portion by distilling said bottom product under an environment in the presence of a polymerization inhibitor in a higher boiling distillation column; measuring concentration of a polymerization inhibitor included in said distillation portion; and controlling the concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said higher boiling distillation column in accordance with said measured concentration of the polymerization inhibitor.
 5. A method of separating and purifying conjugated diene, comprising the steps of: obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor in a lower boiling distillation column; obtaining a second bottom product and distillation portion by distilling said first bottom product under an environment in the presence of a polymerization inhibitor in a higher boiling distillation column; measuring concentration of a polymerization inhibitor included in said first bottom product and second bottom product respectively; controlling the concentration of the polymerization inhibitor included in said first bottom product and/or second bottom product by changing a supply amount of the polymerization inhibitor to said lower boiling distillation column and/or higher boiling distillation column in accordance with said measured concentration of the polymerization inhibitor included in said first bottom product and second bottom product respectively; measuring concentration of a polymerization inhibitor included in said distillation portion; and controlling the concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said higher boiling distillation column in accordance with said measured concentration of the polymerization inhibitor included in distillation portion.
 6. The method of separating and purifying as in any one of the claims 1 to 5 wherein the concentration of the conjugated diene is 90% or more.
 7. The method of separating and purifying as in any one of the claims 1 to 5 wherein the polymerization inhibitor is di-lower alkylhydroxylamine.
 8. The method of separating and purifying conjugated diene as in any one of the claims 1 to 5, wherein weight of the polymerization inhibitor is 0.1 to 200 ppm based on weight of a hydrocarbon mixture including conjugated diene.
 9. The method of separating and purifying conjugated diene as in any one of the claims 1 to 5, wherein a hydrocarbon mixture including conjugated diene is a hydrocarbon mixture including conjugated diene of C4 or more.
 10. An apparatus for separating and purifying conjugated diene, comprising: an distillation column for obtaining a bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor; a measurement means for measuring concentration of a polymerization inhibitor included in said bottom product; a supply system for supplying polymerization inhibitor newly to said distillation column; and a control means for controlling concentration of the polymerization inhibitor included in said bottom product by changing a supply amount of the polymerization inhibitor to said distillation column in accordance with said measured concentration of the polymerization inhibitor.
 11. An apparatus for separating and purifying conjugated diene, comprising: a lower boiling distillation column for obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor; a higher boiling distillation column for obtaining a second bottom product by distilling said first bottom product under an environment in the presence of the polymerization inhibitor; a measurement means for measuring each of concentrations of the polymerization inhibitors included in said first bottom product and a second bottom product respectively; a supply system for supplying the polymerization inhibitor newly to said lower boiling distillation column and/or higher boiling distillation column; and a control means for controlling the concentration of the polymerization inhibitor included in said first bottom product and/or the second bottom product by changing a supply amount of the polymerization inhibitor to said lower boiling distillation column and/or higher boiling distillation column in accordance with said measured concentration of the polymerization inhibitor.
 12. An apparatus for separating and purifying conjugated diene, comprising: an distillation column for obtaining a distillation portion by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor; a measurement means for measuring concentration of a polymerization inhibitor included in said distillation portion; a supply system movable in an up-and-down motion for supplying polymerization inhibitor to said distillation column; and a control means for controlling concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said distillation column in accordance with said measured concentration of the polymerization inhibitor.
 13. An apparatus for separating and purifying conjugated diene, comprising: an lower boiling distillation column for obtaining a bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene; a higher boiling distillation column for obtaining a distillation portion by distilling said bottom product under an environment in the presence of the polymerization inhibitor; a measurement means for measuring concentration of a polymerization inhibitor included in said distillation portion; a supply system movable in an up-and-down motion for supplying polymerization inhibitor to said higher boiling distillation column; and a control means for controlling concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said higher boiling distillation column in accordance with said measured concentration of the polymerization inhibitor.
 14. An apparatus for separating and purifying conjugated diene, comprising: a lower boiling distillation column for obtaining a first bottom product by distilling a hydrocarbon mixture including 80% or more conjugated diene under an environment in the presence of a polymerization inhibitor; a higher boiling distillation column for obtaining a second bottom product and a distillation portion by distilling said first bottom product under an environment in the presence of the polymerization inhibitor; a measurement means for measuring concentration of a polymerization inhibitor included in said first bottom product and second bottom product respectively; a first supply system for supplying the polymerization inhibitor newly to said lower boiling distillation column and/or higher boiling distillation column; a control means for controlling the concentration of the polymerization inhibitor included in said first bottom product and/or second bottom product by changing the supply amount of the polymerization inhibitor to said lower boiling distillation column and/or higher boiling distillation column in accordance with said measured concentration of the polymerization inhibitor included in the first bottom product and the second bottom product respectively; a measurement means for measuring concentration of a polymerization inhibitor included in said distillation portion; a second supply system movable in an up-and-down motion for supplying polymerization inhibitor to said higher boiling distillation column; and a control means for controlling concentration of the polymerization inhibitor included in said distillation portion by changing a supplying stage of the polymerization inhibitor to said higher boiling distillation column in accordance with said measured concentration of the polymerization inhibitor included in the first bottom product and/or the second bottom product.
 15. The apparatus for separating and purifying conjugated diene as in any one of the claims 10 to 14 wherein the measurement means for measuring said concentration is a liquid chromatograph analyzing apparatus or a gas chromatograph analyzing apparatus. 